1. Field
One embodiment of the present invention generally relates to a disk drive using a magnetic disk medium storing servo information including a phase-difference servo burst pattern, in particular, a disk drive using a magnetic disk medium adopting a discrete track storing method.
2. Description of the Related Art
Generally, in disk drives typified by hard disk drives, servo information necessary for positioning control of a head writing data on a magnetic disk medium (hereinafter simply referred to as “disk medium”) and reading data from a magnetic disk is stored in advance on a disk medium. In other words, a disk medium storing servo information is inserted in the disk drive.
Servo information is used for detecting the position of the head. Servo information mainly comprises a cylinder address code for identifying a cylinder (track) position of on a disk medium, and a servo burst pattern for detecting a position in a cylinder. Specifically, servo burst pattern is information for detecting off-track amount (position error) with respect to the center of a cylinder.
As an example of the servo burst pattern, there is phase-difference servo burst pattern adopting a method of detecting phase difference (for example, refer to Jpn. Pat. Appln. KOKAI Publication Nos. 2005-100611 and 8-221919). The phase-difference servo burst patterns disclosed in these documents do not have any special technical meaning with respect to the inclination direction and the angle, and are recorded on a disk medium by magnetic transfer.
In the meantime, recently, disk media having a structure named “discrete track medium (DTM)” (hereinafter referred to as “DTM structure” have received attention. In disk media adopting the DTM structure, regions effective as a magnetic recording section and regions not effective are formed on a surface thereof. The effective regions are projecting magnetic regions provided with a magnetic film. The non-effective regions are non-magnetic regions, or depressed regions where magnetic recording is impossible. Specifically, the non-effective regions include regions that are substantially formed as non-magnetic regions as being depressed, even with a magnetic film.
A disk medium having the above DTM structure is manufactured by a stamper method including a pattern transfer step, and thus can record servo information with high efficiency without using a conventional servo track writer. This recording method is sometimes called “Discrete Track Recording” (DTR). Specifically, adopting the DTR method enables high-accuracy embedded recording of servo information including phase-difference servo burst pattern on a disk medium by a pattern transfer step.
In the above DTR method, it is possible to greatly improve linear recording density, by setting the playback head width by a read head (for example, a GMR head) for reading servo information and user data to be almost the same as the data track pitch width. Data tracks are regions for recording user data, and adjacent to the servo region.
In the meantime, in the case of narrowing the playback head width of the read head with increase in the recording density, the playback head width in the DTR method is almost equal to the data track pitch width, and the cycle of the phase-difference servo burst pattern of the servo information is increased, as described above. Therefore, it is necessary to strictly control the inclination direction and the inclination angle of the phase-difference servo burst pattern. The meaning thereof is explained below.
In disk media having a common uniform magnetic structure other than the DTM structure, when user data is recorded with high density, spread occurs in the transverse direction of the magnetic domain recorded by the write head. To prevent interference with existing data in the adjacent track, a recording width of the write head being 80% or less of the data track pitch is generally adopted. Further, the playback head width is equal to or less than 80% of the write head recording width, for the purpose of playing back a recording signal having the transverse spread with a good S/N ratio. Specifically, drives using disk media having a common uniform magnetic structure adopt a very narrow read head having a playback head width of 64% or less of the data track pitch.
However, in the case of adopting the DTR method, the playback head width of the read head is almost the same as the width of the data track pitch, as described above. In this case, the playback accuracy of the phase-difference servo burst pattern by the read head deteriorates in a certain inclination direction and a certain inclination angle of the phase-difference servo burst pattern included in the servo information, and there is the problem that a sufficient position detection accuracy cannot be obtained for the head.